1. Field of the Invention
This invention relates to electrical switching apparatus especially such as power circuit breakers, network protectors and switches used in low voltage electric power circuits carrying large currents. More particularly, it relates to such apparatus having a manually or electrically operated ratchet mechanism which charges the large spring used to close the switching apparatus.
2. Background Information
Electrical switching apparatus for opening and closing electric power distribution circuits typically utilize an energy storage device in the form of one or more large springs to close the contacts of the device into the large currents which can be drawn in such circuits. Such electrical switching apparatus includes power circuit breakers and network protectors which provide protection, and electrical switches which are used to energize and deenergize parts of the circuit or to transfer between alternative power sources. These devices also include an open spring or springs which rapidly separate the contacts to interrupt current flowing in the power circuit. These open springs are charged during closing by the close spring which, therefore, must store sufficient energy to both overcome the mechanical and magnetic forces for closing as well as charging the open springs. As indicated, either or both of the close spring and open spring can be a single spring or multiple springs and should be considered as either even though the singular is hereafter used for convenience.
An operating mechanism mounts and controls the charging and discharge of the close spring. One type of such operating mechanism includes a cam member which rotates in a single direction and is coupled to the close spring to charge the spring as the cam is rotated either manually, by handle, or automatically, by a motor, through a ratchet mechanism. As the close spring becomes fully charged, the cam goes overcenter and the stored energy in the spring tends to drive the cam. A close prop holds the spring in the charged state.
Typically, a stop member is provided for engaging ratchet teeth of the ratchet mechanism to prevent reverse rotation of the ratchet mechanism during charging and until the cam goes overcenter and is held by the close prop when the close prop is in an unlatched position (where the close prop is disengaged from the cam member so that the cam member is free to be rotated by the close spring). The stop member is also typically in engagement with the ratchet teeth of the ratchet mechanism when the close prop is in a latch position (where the close prop engages the cam member and prevents rotation of the cam member). The engagement between the stop member and the ratchet teeth of the ratchet mechanism, both when the close prop is in the unlatched and latched position, results in friction or a drag force between the stop member and the ratchet mechanism. This drag force increases the release force required for the close prop, particularly when larger close springs are used to increase the current rating. There is room, therefore, for improvement in such electrical switching apparatus and particularly in the manner in which the stop member cooperates with the ratchet mechanism.
There is a need for improved electrical switching apparatus having a stop member for cooperating with a ratchet mechanism that minimizes friction or drag force therebetween during initiation of a closing operation of the electrical switching apparatus.
There is also a need for an improved charging mechanism for electrical switching apparatus that minimizes friction or drag force in the charging mechanism during initiation of a closing operation of the electrical switching apparatus.